AD9481 Analog Devices, AD9481 Datasheet - Page 18

• Manufacturer Part Number: AD9481
• Description: 8-Bit, 250 MSPS, 3.3 V A/D Converter
• Manufacturer: Analog Devices

Specifications of AD9481

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 250MSPS
• Interface: Par
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p,1 V p-p
• Adc Architecture: Pipelined
• Pkg Type: QFP

AD9481
Fixed Reference
The internal reference can be configured for a differential span
of 1 V p-p (see Figure 34). It is recommended to place a 0.1 µF
capacitor as close as possible to the VREF pin; a 10 µF capacitor
is also required (see the PCB layout for guidance). If the internal
reference of the AD9481 is used to drive multiple converters to
improve gain matching, the loading of the reference by the
other converters must be considered. Figure 34 depicts how the
internal reference voltage is affected by loading.
Table 8. Reference Configurations
SENSE Voltage
AVDD
0.5 V (Self-Biased)
AGND to 0.2 V
1.0085
1.0080
1.0075
1.0070
1.0065
1.0060
1.0055
1.0050
1.0045
1.0040
1.0035
Figure 32. Typical Reference Variation with Temperature
–40
–20
0
TEMPERATURE (°C)
Resulting VREF
N/A (external reference input)
0.5 × (1 + R1/R2) V
1.0 V
20
40
60
80
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Reference
External
Programmable
Internal fixed
–0.1
–0.2
–0.3
–0.4
–0.5
0
0
Figure 33. Internal Fixed Reference (1 V p-p)
10µF
Figure 34. Internal VREF vs. Load Current
0.5
0.1µF
1.0
Differential Span
1 × external reference voltage
1 × VREF (0.75 V p-p to 1.5 V p-p)
1 V p-p
IREF (mA)
1.5
VREF
SENSE
2.0
2.5
3.0